Technical Abstract:
Ammonia (NH3) emissions from beef cattle feedyards represent N loss and can have negative environmental consequences. Models have been developed to estimate NH3 emissions from various livestock production systems; however, little work has been conducted to assess their accuracy for large open-lot feedyards. To validate Manure-DNDC, a process-based biogeochemical model, simulated NH3 flux was compared to emissions data collected from two commercial feedyards in the Texas High Plains. Model predictions were in good agreement with measured observations from both feedyards (p < 0.001), and reflected high sensitivity to variations in air temperature and dietary crude protein level. Predicted mean daily NH3 flux densities for the two feedyards were 43.6 and 55.7 kg NH3-N ha**1 d**1, and were not significantly different from observed data. This indicates that Manure-DNDC can assist with NH3 emissions reporting for commercial feedyards, and can be used to evaluate the effects of management practices on N loss.